| Magnesium alloys have poor plastic deformation ability at room temperature due to their tightly arranged hexagonal structure,while multidirectional forging process can accumulate large strain,regulate and improve the microstructure and properties of materials,and expand the application space of magnesium alloys.It is significant to study the multidirectional forging process of magnesium alloy at room temperature.In this paper,the typical extruded AZ80 magnesium alloy was selected as the research object.Firstly,the wire cut samples were treated with solution treatment at 375?+10h to improve their plasticity.Then,multidirection forging with different passes of deformation(0.05,0.075,0.1)and cumulative deformation was performed at room temperature,and finally aging treatment was performed.The stress,microhardness,EBSD and XRD analysis were carried out on the forged samples,and the metallographic and microhardness analysis was carried out on the forged and aged samples.The changes of microstructure and mechanical properties of AZ80 magnesium alloy under multidirectional forging at room temperature and subsequent aging treatment were studied.The results show that:(1)The true stress of the extruded magnesium alloy is not consistent in the three directions at room temperature,and the true stress is the highest when the extruded magnesium alloy is compressed in the X direction(ED direction).When the cumulative deformation is the same,the greater the deformation is,the greater the true stress will be.When the amount of deformation is 0.05,0.075 and 0.1,the true stress is basically stable after the accumulated deformation reaches 1.5,2.925 and 2.4,respectively,while the hardness increases with the increase of the accumulated deformation.(2)The multidirectional forging at room temperature produces a large number of twins in the grain,most of which are tensile twins,and only a small number of compression twins.The larger the pass deformation is,the easier the compression twins are to be formed,and the more significant the grain cutting and refining effect is.Twins lead to an obvious cylindrical preferred distribution and the generation of a large number of dislocations.Similarly,the larger the pass deformation,the higher the dislocation density in the grain.(3)The multi-direction forging at room temperature has a certain degree of inhomogeneity,that is,the microstructure of each area in the same sample does not converge.Some areas show high dislocation density and extremely concentrated stress,and the microstructure is significantly different from that of other areas.(4)Twins introduced by room temperature multidirectional forging significantly affect the subsequent aging precipitation process.At 175?,fine and dense continuous precipitates are preferentially formed in the twin,and begin to form continuous precipitates in the matrix with the increase of time.At the aging treatment of 225?,continuous precipitates were still formed in the twin at the initial aging stage.With the increase of aging time,a large number of discontinuous precipitates appeared in the twin boundary.The shape of the precipitates gradually changed from long strip to ellipse,which inhibited the generation of continuous precipitates in the twin and formed obvious precipitate-free zone around it.At the same time,the size of the granular precipitated phase in the matrix is very small,about 0.1 m.At 275?,the twin boundary is almost discontinuous precipitates,which also inhibits the formation of continuous precipitates in the twin and forms an obvious precipitation-free zone around it.(5)The peak aging of different samples is closely related to the dislocation density,that is,the higher the dislocation density is at the same aging temperature,the more the second phase precipitates at the peak aging.Compared with the aging temperatures 175?,225? and275?,it is found that there are more second phase precipitates in the grains at 175?. |
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